The development of accelerator mass spectrometry (AMS) dating, which allows a date to be obtained from a very small sample, has been very useful in this regard.Other radiometric dating techniques are available for earlier periods.
It takes 5,730 years for half the carbon-14 to change to nitrogen; this is the half-life of carbon-14.
One of the most widely used is potassium-argon dating (K-Ar dating).
Potassium-40 is a radioactive isotope of potassium that breaks down into argon-40, a gas.
Carbon-14 is an unstable isotope of normal carbon, carbon-12.
Cosmic radiation entering the earth’s atmosphere produces carbon-14, and plants take in carbon-14 as they fix carbon dioxide.